1. Field of the Invention
Embodiments disclosed herein generally relate to clearance control between a magnetic head and a recording medium in a magnetic disk device.
2. Description of the Related Art
The recording density of a magnetic disk device can be improved to the extent that the clearance between the magnetic head and the recording medium is reduced. Lower clearances between magnetic heads and recording media have been introduced as a result of higher recording densities in disk devices. For example, clearance adjustment can be performed in which thermal deformation is used by a thermal flying height control (TFC) actuator mounted in a magnetic head in order to reduce the clearance between a magnetic head and a recording medium.
However, structural errors occur in each magnetic head, including errors in machining the shape of a magnetic slider and errors in assembling the suspension for magnetic heads. These errors cause variations in the clearance of magnetic heads. It is essential at high recording densities to minimize these variations and keep the clearance within a predetermined range.
When a magnetic disk device is manufactured, clearance adjustments are made using an embedded contact sensor (ECS) to keep the clearance within a predetermined range. An ECS is configured using metal film and the electrical resistance changes due to frictional heating when the magnetic head and the recording medium are in contact. This change is detected using a predetermined detection current flowing to the ECS. In the clearance adjustment process, power is applied to the TFC in stages. First, contact between the magnetic head and the recording medium, oftentimes referred to as ‘touchdown’, is detected by the ECS, and in response, the TFC power is subtracted in accordance with the indicated clearance. The TFC power to be applied is then determined so the clearance adjustment arrives at the predetermined optimal clearance.
However, some of the clearance between the magnetic head and the recording medium is caused by environmental factors such as the ambient temperature and atmospheric pressure at which the magnetic disk is being used, and external factors such as contaminants. In a worst case scenario, when read/write performance has deteriorated, physical crashing of the recording medium (i.e., touchdown) may occur due to contact, and the reliability of the disk drive may decline significantly.
Therefore, controls are required to keep the clearance within the predetermined range even when some of these external factors have occurred and the clearance between the magnetic head and the recording medium has changed.